Mobilization of free Ca2+ measured during contraction-relaxation cycles in smooth muscle cells of the porcine coronary artery using quin2

Abstract

Ca2+ mobilization in dispersed smooth muscle cells of the porcine coronary artery was investigated using the fluorescent Ca2+ indicator, quin2. The resting [Ca2+]i was 113 +/- 8 nM (a mean +/- SE), and was independent of intracellular quin2 concentrations. Acetylcholine (ACh; over 10 nM) or caffeine (over 3 mM) transiently increased the intensity of fluorescence, thereby reflecting the elevation of intracellular free Ca2+ (Ca2+ transient), while excess K+ gradually increased and maintained the intensity of fluorescence. Application of EGTA reduced the resting intensity of the fluorescence and blocked the K+-induced Ca2+ transient, but did not suppress the ACh- or caffeine-induced ones. Nisoldipine (0.1 microM) did not affect the resting intensity of the fluorescence. This agent blocked the K+ induced but not the ACh- or caffeine- induced Ca2+ transient. Thus, sources of Ca2+ contributing to the K+ -induced Ca2+ transient differ from those evoked by other agents. The amount of Ca2+, as estimated from the increased Ca2+ transient by caffeine or ACh, was increased in proportion to the excess K+-induced influx of Ca2+.

Regulation of cell calcium and contractility in mammalian arterial smooth muscle: the role of sodium‐calcium exchange.

“…If [Ca2+]i is about 100 nM (DeFeo & Morgan, 1985;Sumimoto & Kuriyama, 1986) and [Na+]i is about 10mm (Jones, 1982) (Harder, 1982), the driving force for Na-Ca exchange will favour Ca2+ efflux from arterial smooth muscle cells as it does in other types of cells (Sheu & Blaustein, 1986). However, when [Ca2+]i is low, the Ca2+ efflux mediated by the exchanger (i.e.…”

“…This Ca2+ is extruded against a large electrochemical gradient, since free intracellular Ca2+ concentration, [Ca2+]i, in resting arterial smooth muscle cells is about 100-200 nm (e.g. DeFeo & Morgan, 1985;Sumimoto & Kuriyama, 1986;Goldman, Wier & Blaustein, 1986), and the resting membrane potential is about -40 to -70 mV (e.g. Johansson & Somylo, 1980;Harder, 1982).…”

Caffeine-induced contraction of rat portal vein and effects of K-depolarization, Na-removal and low temperature.

“…The release of intracellular stored Ca by caffeine has been presented in other vascular smooth muscles (Leijten and Van Breemen, 1984;Sumimoto and Kuriyama, 1986;Kobayashi et al, 1986 ;Sato et al, 1988). This is supported by the result that the contraction by caffeine was depressed by ryanodine which has been known to reduce stored Ca in sarcoplasmic reticulum which is released by caffeine (Ito et al, 1986;Ueno et al, 1987;Hwang and Van Breemen, 1987;Sato et al, 1988;Ahn and Karaki, 1988;).…”

Actions of a newly synthesized nitro-compound, E-4701, on rabbit vascular smooth muscles.

“…To measure the intracellular free Ca using fura-2, dispersed smooth muscle cells of the porcine coronary artery were used (16). Fresh pig hearts were purchased from a local slaughter house and brought to the laboratory in fully oxygenated Krebs solution at room temperature within 20 min.…”

“…Measurements of cytosolic free Ca using fura-2: Dispersed single smooth muscle cells were prepared from the porcine coronary artery by collagenase dispersion pro cedures as described previously (16). Dis persed smooth muscle cells were loaded with 1 W fura-2 acetoxymethyl ester (fura-2/ AM) for 60 min at 33-35°C as was done with quin2 by Sumimoto and Kuriyama (16); i.e., under these conditions, the cytosolic concen tration of fura-2 was 50-100 /€M (basal level).…”